Biophysical methods will be employed to elucidate the structure of recombinant DNA molecules. The biochemical and genetic consequences of the presence of base-pair mismatch containing structures that occur in the DNA of transformed bacteria, including excision events and associated DNA synthesis, will be investigated. In order to elucidate the processes involved in the uptake and function of external DNA we will investigate the structure and fate of virus transfecting DNA in transformable bacteria.